1. Field of the Invention
The present invention relates to a means for turning and displacing a web of endless recording material, in particular a paper web in an electrographic printer. Furthermore, the invention relates to a means in which the web of endless recording material is only displaced in parallel fashion.
2. Description of the Related Art
Means of this sort are important components of an electrographic printer means for printing on strip-type recording media of various widths. A printing means of this sort is for example specified in International Published application No. WO/94 27193. The printer means has an intermediate carrier that operates electrographically, for example a photoconductor drum, with a usable width corresponding to twice the width of a standard form, e.g. DIN A4 or letter size. The additional components, such as the fixing station, the developer station, the cleaning station, etc., are likewise designed with this usable width.
With this known printer means, different types of operation are possible. In monochromatic duplex operation, the web of endless recording material is turned during its transport through the printer means, so that two web segments result: in a first web segment, the front side of the web lies opposite the transfer printing location of a print unit, whereas in a second web segment the back side of the web is simultaneously imprinted at the same transfer printing location. By means of the use of differently colored color particles in different developer units of the print unit, a two-color duplex operation is also possible. In another type of operation, two-color simplex operation, the web is displaced in parallel fashion during transport in the printer means by at least a web width. The displaced web segments are together led past the transfer printing location, in a side-by-side position. As the web first passes by the transfer printing location, image and text elements are printed with a first color; in the second pass of the web, with a lateral displacement, image and text elements are printed with the second color.
For completeness, we also refer to simplex operation and parallel simplex operation. In the first-named simplex operation, a recording medium is imprinted in a conventional way with up to doubled the width of a DIN A4 page or a page with letter size format. In parallel simplex operation, two webs separated from one another, e.g. respectively having a width according to the DIN A4 or letter size format, are guided side-by-side through the printer means and are imprinted.
In the imprinting of a single web that is displaced in parallel in the printer, or is displaced in parallel and also turned, and again supplied to the transfer printing location of the print unit and imprinted, it is to be ensured that the parallel displacement or parallel displacement with simultaneous turning takes place without disturbance and with high precision. With the use of a means for turning and/or for displacement of a web in a high-performance printer that reaches web transport speeds in the range of 0.1 to 2.5 m/s, measures are to be provided that enable a rapid passage of the web, even with the use of foldable endless material with folds.
From the German patent application 94 112 973.6, a turning means is known for strip-type recording media in which diverting elements are arranged in order to divert the web in the shape of a W. The web is guided tautly through the turning means and is in close contact with the diverting units.
From a further German patent application, P 44 35 756.7, a turning means is known for strip-type recording media whose diverting elements form two turning triangles. The turning triangles are arranged so as to be rotated relative to one another by a spread angle, so that the overall turning means takes up little space.
An object of the invention is to provide a means for displacing, or for displacing and turning, a web, which is of simple construction and ensures disturbance-free operation.
This and other objects and advantages are provided by a means for turning and displacing a web of endless recording material by means of a web supply that guides the web along a first transport path from a transport direction, and having a web take-up that carries away the web, displaced by at least a web width, after its circuit about a diverter that is arranged underneath and after the web supply means (as seen in the direction of transport), the web take-up being arranged above the diverter and next to the web supply, whereby a first edge, facing the web take-up, of the supplied web rests loosely on a first guide surface of the diverter, and the web is guided upwards at an angle to the web take-up with this first edge, and on which the side facing the web supply is carried off along a second transport path, approximately in the direction of transport. For a means exclusively for displacing a web, without turning it, this object is solved by means of a web supply that supplies the web along a first transport path from a direction of transport, and having a web take-up that carries off the web, displaced by at least a web width, after it passes through a loosely hanging web loop, the output means being arranged above the web loop and next to the web supply, whereby the web take-up carries away the web along a second transport path, approximately in the direction of transport, with a first edge, facing the web take-up, of the supplied web on the side facing the web supply. Advantageous developments of the invention are provided by diverter having an oblong body whose longitudinal axis runs approximately vertically, and in that the first guide surface is convexly curved. Preferably, the body has a cylindrical lower segment. The body has a second guide surface in its upper region, which surface guides and holds down the second edge, facing the first edge, of the web, when the web climbs up during its circuit about the body and exceeds a predetermined height. The second guide surface is formed by spread-out arms in the manner of a Y, and in that the arms lie within a plane that is at least approximately parallel to the web segment shortly after the supplying by means of the web supply. The arms run spread out at an angle of 30.degree. to 60.degree., preferably 45.degree., from the longitudinal axis of the body.
Alternately, the body is fashioned as a rotational body. The rotational surface of the rotational body is Y-shaped.
As another alternative, the body has, at least in its upper part, the shape of an inverted truncated cone.
The first and the second guide surfaces are adjustable in height. The height adjustment takes place dependent on the required length of the web loop for a loop storage unit.
The preferred web take-up contains a guide element that is arranged approximately in a horizontal plane and that has a guide surface via which the web is guided after passing through the web loop, and the longitudinal axis of the guide surface encloses an angle in the range of 15.degree. to 45.degree., preferably 20.degree., with the longitudinal axis, projected in the horizontal plane, of the web supply means.
The guide surface is convexly curved in one embodiment. The web output contains a diverting element to which the web guided via the guide element is supplied directly, and in that the web is supplied to the diverting element from below, coming from the direction of the guide element, and is diverted in the direction of transport. The guide element can be pivoted by the angle out of a first position, in which the guide surface is arranged parallel to the axis of the diverting element, and can be fixed in this pivoted position.
The guide element, and preferably also the diverting element, each have a stop on the side facing the web supply means, on which stop the edge of the web rests.
The web supply means contains a transport roll, as well as at least one counterpressure roll, between which the web is supplied.
A web guide, which enables a calmed and loose supplying of the web, is arranged underneath the web supply. The web supply has a support surface, preferably concavely curved, with a width that corresponds to at least the width of the web. The web guide contains a movable support element that moves the front side of the web against the support surface with friction. The support element is fashioned by a number of spiral springs arranged next to one another. The support element may instead be fashioned by a felt tab or a material tab.
A guide element is arranged underneath the web supply means, the guide element guiding the front segment of the web during the supply thereof in a predetermined direction, preferably in the direction of an operator. The guide element has a curved support surface for the first segment of the web, as well as a lower contact surface for an edge of the web. The support surface is preferably made of a material that does not become electrostatically charged during the movement of the web.
According to the first aspect of the invention, in which the web is turned and displaced, this web is guided loosely around a diverting means, whereby the first edge is supplied to the diverting means at an angle from the top downward, and there is led upward again from below, coming upward at an angle. The edge rests on the first guide surface of the diverting means, so that a loop forms naturally from the web supply means up to the web output means. Since this first edge rests loosely on the first guide surface, the web loops can describe excursion movements in the vertical direction, thus compensating for fluctuations in the transport speed in the area of the diverting means. Such fluctuations can for example arise due to changes in the friction relationships, or due to the formation of folds. The invention is suited both for webs of endless material without folds running transversely and also for webs with folds (such as fan-fold webs).
In the invention, the web surfaces come into frictional contact with only a few elements. In this way, the risk of web jamming due to different frictional conditions, or damage to the web, is reduced. The surfaces of the mechanical guides that are in contact with the web can be provided with very low-friction surfaces, or can be made resistant to wear by means of a surface treatment. The operational reliability of the means is thereby further increased.
In practice, it has turned out that web speeds of up to 2.5 m/s and higher are under control, and the requirements for use in high-performance printers are fulfilled. In the upper web speed range, the web run is particularly stable.
The first guide surface is preferably convexly curved. It is thereby adapted to the curvature of the geometry of the web loop, which geometry forms automatically due to the weight of the web and its elasticity; the first guide surface supports the natural loop formation.
An exemplary embodiment of the invention is characterized in that the oblong body of the diverting means has in its upper region a second guide surface that guides and holds down the second edge--lying opposite the first edge--of the web when the web climbs up in its motion around the body and exceeds a predetermined height. By means of these measures, the vertical excursion motion of the loop on the loop base is limited to a predetermined measure. If, due to a disturbance, the uniformity of the web transport is disturbed, e.g. due to buckling in of the web at the fold points of a fan-fold web, the web loop is shortened, which is expressed in a climbing up of the web at the first guide surface. Past a predetermined height, the upper, second edge of the web comes to rest on the second guide surface, whereupon the tensile stress on the second edge of the web is increased, and the web becomes taut, and thereby unfolds. Disturbances during the passage of the web are thus automatically compensated.
According to a further exemplary embodiment of the invention, the first and second guide surfaces can be adjusted in height. By this means, on the one hand the diverting means can be adapted to different widths of the web. On the other hand, the height adjustment enables adaptation to the length of the web loops from the web supply means to the web output means. This web loop also serves as a web storage means whose length is set dependent on the utilized length format of the pages of the web, and is predetermined by the printer controller or by the operating personnel.
According to a further aspect of the invention, a means for displacing a web of endless recording material is provided, having a web supply means that supplies the web along a first transport path from a direction of transport, and having a web output means that carries off the web, displaced by at least a web width, after it passes through a loosely hanging web loop, the output means being arranged above the web loop and next to the web supply means, whereby the web output means carries away the web along a second transport path, approximately in the direction of transport, with a first edge, facing the web output means, of the supplied web on the side facing the web supply means. In this means, no turning of the web takes place. The means is constructed in such a way that the web forms a loop that hangs loosely. The web is thereby guided in such a way that the first edge--facing the web output means--of the supplied web is carried away, on the side turned away from the web supply means, along a second transport path, approximately in the transport direction. The upper side of the web on the second transport path and the upper side of the web of the first transport path align with one another. This means is thus used for two-color simplex operation.
The solution of the problem posed according to this aspect of the invention is surprisingly simple, and the web loop that forms naturally due to the force of gravity enables displacement by at least a web width. Due to the weight of the web, the web loop remains stable in shape even at high transport speed. Both webs provided with folds and also smooth webs can be transported and displaced.
In a preferred exemplary embodiment of the invention, the web output means contains a guide element--arranged at least approximately in a horizontal plane--with a guide surface via which the web is guided after passing through the web loop, whereby the longitudinal axis of the guide surface encloses an angle in the range from 15.degree. to 25.degree., preferably 20.degree., with the longitudinal axis of the web supply means, projected in the horizontal plane. Due to its angled arrangement, this guide element enables the natural loop shape to be maintained, and enables the avoidance of small curvature radii during diversion into the transport path displaced in parallel fashion, which small radii can cause the formation of folds. With the use of folded recording material, the guide element prevents buckling of the web at the folds.
In order to avoid creasing or formation of folds in the recording material, the web leaving the guide element is supplied from below directly to a diverting element, which diverts the web in the direction of the web loop. The diverting element has a longitudinal axis that is at least approximately parallel to the longitudinal axis of the web supply means. The diverting element prevents a curvature of the web that can result due to the displacement of the web by at least a web width.
In an exemplary embodiment, the guide element, and preferably also the diverting element, can each have a stop on the side facing the web supply means, an edge of the web resting on this stop. Defined edge positions of the web, and a precise guiding, thus result during print operation.